KR101295418B1 - Projection exposure method, projection exposure apparatus, laser radiation source and bandwidth narrowing module for a laser radiation source - Google Patents

Abstract

에 따른 수차 파라미터 α 및

에 따른 코히어런스 시간 τ를 특징으로 한다. 레이저 방사는 마스크에 지향되는 조명 방사를 생성하기 위해 조명계내로 도입되고, 패턴이 투영 대물렌즈의 조력으로 기판상으로 이미징(imaging)된다. 상기 스펙트럼 강도 분포는, 선 형상 파라미터 ατ²에 대해서, 조건 ατ² ≤ 0.3이 참이도록 설정된다. 결과적으로, 이미지 생성에 대한 시간적으로 변화하는 얼룩의 영향이 일반적인 방법에 비해, 이미지 생성에 대한 색수차의 영향을 동시에 증가시키지 않고, 감소될 수 있다.A projection exposure method for exposure of a radiation-sensitive substrate in which a mask of a pattern of at least one image is arranged in an area of an object plane of a projection objective lens, the projection exposure method comprising: Laser radiation with a spectral intensity distribution I (ω) is used. Laser radiation,

Aberration parameters α and

It is characterized by the coherence time τ according to. Laser radiation is introduced into the illumination system to produce illumination radiation directed at the mask and the pattern is imaged onto the substrate with the aid of the projection objective. The spectral intensity distribution is set so that the condition ατ ² ≦ 0.3 is true for the linear parameter ατ ² . As a result, the effect of temporally varying blobs on image generation can be reduced, without simultaneously increasing the effect of chromatic aberration on image generation, compared to the conventional method.

Description

PROJECTION EXPOSURE METHOD, PROJECTION EXPOSURE APPARATUS, LASER RADIATION SOURCE AND BANDWIDTH NARROWING MODULE FOR A LASER RADIATION SOURCE}

The invention relates to a radiation-sensitive substrate in which a mask of a pattern of at least one image is arranged in an area of the image surface of the projection objective lens arranged in an area of the object surface of the projection objective lens. A projection exposure method for exposing a substrate, a projection exposure apparatus suitable for performing the method, and also a bandwidth narrowing module for a laser radiation source and a laser radiation source.

Today, microlithographic projection exposure methods are commonly used to fabricate semiconductor components and other microstructured devices. In this case, a mask (reticle) with a pattern of the structure to be imaged, such as a line pattern of a layer of a semiconductor component, is used. The mask is illuminated in the illumination radiation provided by the illumination system and positioned in the projection exposure apparatus between the projection objective lens and the illumination system in the region of the object plane of the projection objective lens. The radiation and pattern changed by the mask pass through the projection objective, which projects the pattern of the mask onto the substrate to be exposed, which generally has a radiation-sensitive layer (photoresist).

Current projection exposure apparatuses for high resolution microlithography in deep or very deep ultraviolet regions (DUV or VUV) generally use lasers as the main light source. In particular, KrF excimer lasers with an operating wavelength of approximately 248 nm or ArF excimer lasers with an operating wavelength of approximately 193 nm are common. An F ₂ laser is employed for an operating wavelength of 157 nm and an Ar ₂ excimer laser can be used at 126 nm. The main laser radiation source emits a laser beam consisting of laser light that has been reshaped to produce illumination radiation received by the connected illumination system and directed onto the mask. The spectral characteristics of the illumination radiation and of the projection radiation, ie their properties depending on the wavelength λ or the angular frequency ω, are in this case substantially determined by the spectral characteristics of the main laser radiation.

In the design of the lithographic process, the line width of the structure on the reticle is adapted such that after imaging by the assistance of the projection objective lens using illumination assumed to be known, the sizes of the required structure in the photosensitive layer are exposed. In this case, the same structure of the mask to be imaged identically in the photoresist, independent of the position of the substrate, is important. Otherwise, in the case of semiconductor components, there may be a loss of speed or, in the worst case, even a functional loss. One important variable in semiconductor manufacturing is therefore the change in the thickness (CD) of the critical structure, which is brought about by the process and also referred to as the "critical change of dimension" or "CD change". Thus, the uniform width, so-called CD uniformity, of the same structure imaged over the field constitutes an essential quality criterion of the lithographic process.

The determining factor for the width of the structure in the photoresist is the radiant energy deposited there. Customary approximations are assumed in which the photoresist is exposed above a certain deposition amount of radiant energy, and not below that amount. Limits on the amount of radiant energy are also expressed as “resist thresholds”. What is important in this case is the radiation intensity which is incorporated during the total exposure time at the location on the substrate. The magnitude of the radiant energy deposited at a particular location of the photoresist depends on a number of influence variables, inter alia, optical aberration, in particular chromatic aberration, the polarization state of exposure radiation, and also stray light and double reflection. If a laser is used as the main light source, the so-called effect of speckle, which can occur as a result of self-interference when at least partially using coherent radiation, can be added as an additional potential due to CD changes. have. So-called temporally varying stains (dynamic stains, temporal stains) are of primary importance here, which is the time resulting from the use of a light source with a coherence time that is not much shorter than the duration of the laser pulse. Caused by fluctuations in intensity. In contrast, the coherence time of a typical coherent light source is so short that spots that change in time do not matter in that case.

Many influence parameters must be taken into account when selecting an appropriate laser radiation source for a microlithographic projection exposure apparatus. In particular, in the case of a high resolution projection objective having a large image field, chromatic aberration is very complicated. If the projection objective is not completely chromaticly corrected, radiation with different wavelengths creates different focal positions in the image field of the projection objective for each wavelength. In order to avoid the resulting disadvantages, one generally tries to use a very narrow band of radiation sources. A typical excimer laser thus includes a bandwidth narrowing module that narrows the inherent emission spectrum of the hundreds of pms lasers by tens of squares, eg, with a bandwidth less than 1 pm. Large bandwidths are therefore disadvantageous in terms of chromatic aberration. In contrast, large bandwidths are advantageous with regard to the appearance of dynamic blobs, since the undesired interference phenomena represented as blobs are due to the temporal coherence of the light. Since light is less coherent, more different wavelengths are included in the laser radiation, and a large bandwidth is advantageous with regard to avoiding spotting.

Thus, the selection of the appropriate bandwidth always compromises between the demands for less chromatic aberration on one side and less speckle on the other. Setting the optimum bandwidth is a technical problem that must be determined when designing each projection exposure apparatus based on available data, for example for chromatic correction of the projection objective lens.

Patent applications US 2006/0146310 A1 and US 2008/0225921 A1 disclose in each case a projection exposure method and a projection exposure apparatus in which the spectral intensity distribution of the laser radiation source used can be set or changed.

The object of the present invention is designed to reduce the influence of temporally varying blobs on image generation in comparison with conventional systems and methods, without simultaneously increasing the effect of chromatic aberration on image generation, and with laser as the main light source. It is to provide a projection exposure method and a projection exposure apparatus designed to carry out the method, which operate in conjunction. It is also an object of the present invention to provide an appropriate laser radiation source and also a bandwidth narrowing module for a laser radiation source for carrying out the projection exposure method.

This object is achieved by a projection exposure method comprising the features of claim 1, by a projection exposure apparatus comprising the features of claim 6, and also by a laser radiation source comprising the features of claim 11 and the features of claim 14. A bandwidth narrowing module is included. Advantageous developments are detailed in the dependent claims. Representation of all claims is incorporated by reference in the context of the detailed description.

Through the proper setting of the spectral shape of the laser line, i.e. through the setting of the spectral intensity distribution of the laser radiation emitted by the main laser radiation source, the effect of the laser radiation source on the chromatic aberration and the influence of the laser radiation source on the appearance of dynamic speckles It has been recognized that it may affect the balance, in a targeted manner.

Setting the appropriate spectral shape of the laser line results in degrees of freedom that have not been considered so far in the design of lithographic apparatus and processes.

The spectral intensity distribution of the laser lines used has two opposite effects on the lithography process: wide laser lines increase chromatic aberration, and narrow laser lines can lead to long coherence times resulting in severe dynamic staining. Until now, substantially only chromatic aberration has been a driver in laser roadmaps. Therefore, considerable efforts have been made to develop laser radiation sources with the narrowest possible bandwidth. In order to achieve the original true reading with only an acceptable low CD change, it was recognized that the dynamic staining should also be significantly reduced, so that both effects should be considered.

The systematic description of the present invention as shown above describes how dynamic spots can be minimized by fitting the spectral shape of the laser line without aggravating chromatic aberration in the process. This can be understood as follows.

에 기초하여, 모든 관련된 상황에 대해서 여기서 dλ 및 dω는 비례적임으로써(

), 각주파수 및 파장이 완전히 동등한 기호법이다. 또한, 이하에서는, 레이저 선이 각주파수 ω=0에서 그 중심을 갖는 것으로 가정되며, 그게 아니라면, 후술되는 방정식 (1)과 그 다음에 있어서 (ω-ω₀)²는 ω²를 대신하여 매회 기입되어야 할 것이다.Let I (ω) be the spectral shape of the laser line. Because of the simpler notation, the angular frequency ω is used instead of the wavelength λ below. Speed of light with c ₀

Based on, where for all relevant situations dλ and dω are proportional (

), Each frequency and wavelength are completely equivalent notation. In addition, in the following, it is assumed that the laser line has its center at the angular frequency ω = 0, and if not, the equation (1) described below and then (ω-ω ₀ ) ² each time replaces ω ² . It will have to be filled out.

Chromatic aberration (or its effect on the lithographic process) is proportional to the second moment of the spectral distribution, ie

In contrast, dynamic staining is determined by temporal autocorrelation μ (Δt). Coherence time τ

에 의해

By

Is calculated.

Dynamic staining becomes weaker because a small coherence time τ can affect the averaging over more static independent radiation distributions in the laser pulse. Autocorrelation can be calculated from the spectral intensity distribution normalized by Fourier transform (FT),

As is known, the Fourier transform maintains the L ₂ norm, and equation (2)

에 등가이다.

Is equivalent to

For the lithographic process, therefore, equations (1) and (4) are optimal when as few spectral line shapes I (ω) are used as possible. From the unit consideration, it is directly clear that the dimensionless product ατ ² is a relevant variable, ie, the smaller its product ατ ² is, the more suitable it is for the lithographic process. Since this product parameterizes the spectral shape of the laser line, the product is also denoted below as “linear shape parameter” ατ ² or simply “shape parameter” ατ ² .

In some embodiments, for the linear parameter ατ ² , the condition ατ ² <0.1 is true. In particular, the condition ατ ² ≦ 0.09 or ατ ² ≦ 0.08 can be satisfied.

For further understanding of the background, several principles regarding the line width and profile of the spectral lines should be mentioned first. In the emission of electromagnetic radiation based on the transition between two energy levels of the atomic system, the frequency of the corresponding spectral lines is not strictly a single wavelength. The frequency distribution of the intensity of the emission intensity around the center frequency is observed. The frequency spacing between these two frequencies at half the maximum intensity present at the center frequency is called full width at half maximum (“FWHM”). The term "bandwidth" is also used for full width at half maximum in these applications. In general, the spectral region within the full width at half maximum is represented as a line core, and the regions on both sides of the outside of the line core are represented as a line wing.

The excited intraatomic electrons again emit their excitation energy in the form of electromagnetic radiation (natural emission). During spontaneous emission, the atoms do not emit strictly single wavelength radiation, but rather the emitted radiation has a frequency-dependent internal distribution. Without external influences, the atoms emit radiation with a so-called "natural linear shape" described by the Lorentz profile. The full width at half maximum of the Lorentz profile is the natural line width of the so-called emission process.

However, in the area of laser physics, the Lorentz profile is a rough approximation that is valid only near the center of the line, i.e. around the center frequency. A realistic approach widely used in laser physics is that of a modified Lorentz curve which can serve as a realistic criterion for comparison of different laser shapes. This will be explained in great detail in the detailed description of the preferred exemplary embodiments.

는 가우스 곡선의 경우에 있어서 참이다. 스펙트럼 강도 분포 I(ω)는, 가우스 곡선을 측정된 강도 프로파일에 맞추는 것에 있어서, 작은 편차 또는 오차, 예컨대, 10% 미만의 또는 8% 미만의 또는 5% 미만의 또는 2% 미만의 오차만이 발생하는 경우에 특히 가우스 곡선에 실질적으로 대응한다.In the case of the modified Lorentz curve, a significant reduction in the linear parameter ατ ² compared to the linear shape parameter can be achieved when the spectral intensity distribution I (ω) substantially corresponds to a Gaussian curve of width σ, where α = σ ^2/2 and

Is true in the case of a Gaussian curve. The spectral intensity distribution I (ω) is such that only a small deviation or error, such as less than 10% or less than 8% or less than 5% or less than 2% in fitting the Gaussian curve to the measured intensity profile In particular it substantially corresponds to a Gaussian curve.

Further reduction of the linearity parameter ατ ² is possible when the spectral intensity distribution I (ω) has a parabolic shape. The spectral intensity distribution I (ω) is a small deviation or error, such as less than 15% or less than 10% or less than 8% or less than 5% or less than 2%, in fitting the parabola to the measured intensity profile. In the case where only an error of? Occurs, it substantially corresponds to the parabolic shape. Compared to Gaussian curves or modified Lorentz curves, in the case of parabolic shapes there is also less radiation energy in the region of the line wing and correspondingly more radiation energy in the region of the line core, which is responsible for chromatic aberration and blotches. It has proved to be advantageous in terms of optimization. In particular, the side of the parabolic intensity profile does not have an inflection point in profile I (ω), which, in the case of a parabolic profile, causes relatively large amounts of energy to lie in the area of the line core and relatively less energy to the line wing It is very clear that we are in the realm of.

The invention also relates to a projection exposure apparatus comprising a main laser radiation source for emitting laser radiation, wherein condition ατ ² ≤ 0.3 is true.

The invention also relates to a laser radiation source for emitting laser radiation wherein the condition ατ ² ≦ 0.3 is true.

The invention also relates to a bandwidth narrowing module for a laser radiation source, wherein the bandwidth narrowing module is designed such that the laser radiation source equipped thereon emits laser radiation in which the condition ατ ² ≤ 0.3 is true.

The foregoing and additional features are not evident solely from the claims, and the individual features may be in the form of a plurality of subcombinations by themselves in each case or in embodiments of the invention and in other fields. It also emerges from the description and the drawings, which can be realized as and which can achieve advantageous and inherently protected protective embodiments. Exemplary embodiments of the invention are illustrated in the drawings and described in more detail below.

The present invention is designed to reduce the influence of temporally varying blobs on image generation as compared to conventional systems and methods, without simultaneously increasing the effect of chromatic aberration on image generation, and operating in conjunction with a laser as the main light source. The projection exposure method and the projection exposure apparatus designed to implement the method can be provided. Furthermore, the present invention can provide a laser radiation source suitable for carrying out the projection exposure method and also a bandwidth narrowing module for the laser radiation source.

1 schematically shows the configuration of a projection exposure apparatus for microlithography.
FIG. 2 shows a schematic spectral line profile of the laser in FIG. 2A and the effect of the finite spectral bandwidth of the laser radiation source on the focal position when using a projection objective that is not completely chromaticly corrected in FIG. 2B.
3 shows a diagram relating to the spectral characteristics of laser radiation of a general laser.
4 schematically shows different possible spectral line shapes of laser radiation.
5 schematically shows the configuration of an excimer laser with a bandwidth narrowing module.

1 can be used in the manufacture of semiconductor components and other elaborately structured devices and operates in conjunction with electromagnetic radiation or light from the deep ultraviolet range (VUV) to obtain resolutions below 1 micrometer of moisture. An example of the microlithography projection exposure apparatus 100 is shown. An ArF excimer laser having an operating wavelength of approximately 193 nm serves as the main light source 102, and the linearly polarized laser beam of the laser is coupled into the illumination system 190 coaxially with respect to the optical axis 103 of the illumination system. Other UV laser radiation sources such as F ₂ lasers with an operating wavelength of 157 nm, or KrF excimer lasers with an operating wavelength of 248 nm are likewise possible.

The polarized light from the light source 102 first enters the beam expander 104, which serves to reduce coherence and increase the beam cross section, for example. The magnified laser beam includes a plurality of optical components and groups, and on the downstream pupil shaping surface 110 of the illumination system 190, also locally represented as a second light source or also as an “illumination pupil”. Enter into pupil shaping 150, which is designed to produce a (two-dimensional) illumination intensity distribution. The pupil shaping plane 110 is the pupil plane of the illumination system.

The pupil shaping unit 150 may be set in various ways such that different local illumination intensity distributions (ie, second light sources of different structures) can be set in accordance with the driving of the pupil shaping unit. 1 schematically shows by way of example a general setup (CON) with various illuminations of a circular illumination pupil, ie centralized, circular illumination spot, dipole illumination (DIP) or quadrupole illumination (QUAD).

It is an optical raster element 109 which is arranged in close proximity to the pupil-shaped screen 110. Coupling-in optical unit 125 arranged downstream of the latter is arranged with a reticle / masking system (REMA) 122, which serves as an adjustable field stop. Light propagates onto an intermediate field plane 121 which is present. Optical raster element 109, also referred to as a field-defining element (“FDE”), has a two-dimensional array of diffractive or refractive optical elements, and emits incident radiation in the region of field surface 121. In order to illuminate the rectangular illumination field after passing through the downstream coupling-in optics 125. The radiation is further homogenized by the superimposition of the partial beam bundles, so that the FDE acts as a field shaping and homogenizing element.

The downstream imaging objective 140 (also referred to as the REMA objective) may place the intermediate field face 121 into the field stop 122, for example, between 2: 1 and 1: 5, and this embodiment Imaging on reticle 160 (mask, lithographic original) at a scale that is approximately 1: 1 in.

These optical elements that receive light from the laser 102 and take shape from light illumination radiation directed onto the reticle 160 belong to the illumination system 190 of the projection exposure apparatus.

Arranged downstream of the illumination system is an optical axis 103 such that the pattern arranged on the reticle lies on the object face 165 of the projection objective 170 and in this way with the aid of the scan drive for scanner operation. It is a device 171 for holding and manipulating the reticle 160 so that it can be moved in the scan direction (y direction) perpendicular to the (z direction).

Downstream of the reticle face 165, serves as a reducing objective, and the image of the pattern arranged in the mask 160 on a reduced scale, for example on a scale of 1: 4 or 1: 5, Followed by a projection objective 170 for imaging onto a wafer 180 coated with a photoresist layer, the photosensitive surface of the wafer lying on the image plane 175 of the projection objective 170. Refractive, reflective or reflective projection objectives are possible. Other reduction scales, such as more reductions up to 1:20 or 1: 200, are also possible.

The substrate to be exposed, which in the example case is the semiconductor wafer 180, is held by a device 181 including a scanner drive to move the wafer synchronously with the reticle 160 perpendicular to the optical axis. Depending on the design of the projection objective 170 (eg, with no intermediate image or with an intermediate image folded or unfolded), this movement may be valid in a side by side or non-parallel manner with respect to each other. Device 181, also represented as a “wafer stage”, and device 171, also represented as a “reticle stage”, are part of a scanner device controlled by a scan control device.

The pupil shaped screen 110 is placed at or near the optically coupled position with respect to the nearest pupil plane 145 and with respect to the image side pupil plane 172 of the projection objective lens 170. Thus, the spatial (local) light distribution in the pupil 172 of the projection objective lens is determined by the spatial light distribution (spatial distribution) in the pupil shaping plane 110 of the illumination system. Between the pupil planes 110, 145, 172, field planes, which are Fourier-transformed planes with respect to the individual pupil planes, respectively, lie in the optical beam path. This is especially true of the downstream field face 121, in which the defined spatial distribution of illumination intensity on the pupil shaped screen 110 eventually corresponds to a specific angular distribution of illumination radiation incident on the reticle 160. Make a specific angular distribution of illumination radiation in the area.

The laser radiation source 102 emits laser radiation with a specific spatial intensity profile I (ω) according to the wavelength λ or according to the angular frequency ω. The effects of the use of a light source with a finite bandwidth on image quality when using a projection objective lens that is not fully chromaticly corrected are outlined with reference to FIG. 2.

는 반치전폭(FWHM)으로 불린다. 레이저 선이, 총 신호에 대한 상이한 강도들의 원인이 되는 상이한 파장들을 포함한다는 것이 명백하다. 반치전폭내의 스펙트럼 영역은 라인 코어로도 나타내어지며, 외부의 영역들은 라인 윙으로서 나타내어진다.For this purpose, FIG. 2A schematically shows the spectral intensity profile I (ω) of the laser radiation source LS. The maximum intensity, I _0, is at the center frequency ω ₀ . Frequency spacing between two frequencies ω ₁ and ω ₂ where intensity drops to half of maximum

Is called full width at half maximum (FWHM). It is clear that the laser line contains different wavelengths which cause different intensities for the total signal. The spectral region within full width at half maximum is also represented by the line core, and the outer regions are represented as the line wings.

FIG. 2B shows an optical axis OA representing an imaging system for imaging a pattern PAT lying on an object plane OS of a projection objective into an area of the image plane IS that is optically coupled with respect to the object plane. The projection objective PO with the two lens elements L1, L2 arranged coaxially with respect to An aperture stop AS defines an effective image side numerical aperture NA of imaging and is arranged in the vicinity of the pupil plane of the objective lens. The pattern PAT of the mask comprises the illumination light provided by the illumination system at the outer edge of the beam path, which is bounded by the aperture aperture, a diffraction order of +1 order and also of -1 order. It is schematically illustrated as a diffraction grating which diffracts at zero diffraction orders along the optical axis.

The broadband laser radiation source LS emits radiation with different wavelengths with different intensities, where, depending on the colors of the light in the visible spectral region, the average wavelength is expressed as "g" for "green" and maximum The wavelength is shown as "r" for "red" and the minimum wavelength is shown as "b" for "blue". It goes without saying that the ratios for the wavelengths from the far ultraviolet region below 260 nm should be correspondingly applied. In the case of non-chromaticly corrected systems, the focal plane of the relatively shorter wavelength (b) then lies closer to the optics, and the relatively longer wavelengths (g) and (r) are more from the projection objective. Far progressively focused. However, the substrate to be exposed, such as a semiconductor wafer, can be precisely brought into the focal region only with respect to one of the wavelengths, and the focal positions of the other wavelengths then lie outside the surface to be exposed.

The focal position changes linearly with the first approximation with respect to the wavelength (in the case of chromaticly corrected objectives this effect will only be secondary to the wavelength). The change in critical dimension (ΔCD) thus appears secondary with the change in wavelength. It is evident that the chromatic aberration, or its effect on the lithographic process, is proportional to the second moment of the spectral distribution, parameterized by the aberration parameter α, for the purposes of this application, which is true:

 Along with the wavelength dependency of the focal position as described in greater detail herein, chromatic aberration also includes the wavelength dependency of the magnification scale. This effect is also included by the aberration parameter α.

The second influence variable under consideration here that affects the lithographic process is dynamic staining. Spots occur as a result of uncontrolled or uncontrolled interference between different parts of the laser beam. The interference causes quenching at some points corresponding to a contrast of 100%. The exact shape of the blob pattern depends on the phase association of the different parts of the laser beam that change over time. This temporal intensity wave is referred to as "temporal stain" or "dynamic stain" in the technical literature. If only the possibility of reducing the contrast in these cases is present in the superposition of many different blob patterns during the duration of the laser pulse, this leads to a problem of how to quickly change the blob pattern. Multiple independent blob patterns result from the duration of the laser pulse, which is divided by the phase correlation time of the laser radiation. The correlation time eventually results from different frequencies of light in the laser radiation, ie it relates to the linear shape of the emitted intensity spectrum. For the purpose of this application, the correlation time or coherence time τ results from the following equation:

The equation above indicates that there is a relationship between the temporal coherence of the light source and its spectral bandwidth. If both variables are validly defined, it is clear that the variables are inversely proportional to each other. In addition, more intensity analysis indicates that the spectral shape of the radiation emitted by the light source also affects this relationship.

The aberration parameter α is proportional to the square of the bandwidth, and the coherence time τ is proportional to the inverse of the bandwidth. One important conclusion from this insight is that the product ατ ² is bandwidth independent. This in turn means that the bandwidth of the laser radiation source for the lithography process can be selected based on the technical parameters and the spectral line shape, which is parameterized by the linear parameter ατ ² , is dependent on the influence and chromatic aberration of the radiation source on the generation of dynamic blobs. In order to achieve an optimization between the effects of the radiation source on the surface, it means to remain free parameters.

The magnitude of the linear shape parameters will now be described in greater detail below for various laser linear shapes.

In the textbook, the spectral shape of the laser line is often described as the Lorentz profile:

However, this is only a rough approximation that is valid close to the center of the line. A more advantageous approach widely used in laser physics is that of a modified Lorenz curve.

It is necessary that v> 3 so that the chromatic aberration α does not diverge, that is, optical lithography is possible anyway. About chromatic aberration, then

This is obvious,

About coherence time

This is obvious.

The value for v can be calculated from the FWHM (full width at half maximum) and the E95 value (95% of energy is in this frequency range). These values can thus be accessed via stereoscopic measurement techniques.

0.083)임으로써, ν=4.5를 넘어서는 약간의 개선만이 달성될 수 있다.From the measurement data for the XLA-360 laser as the reference laser, it was found that, for example, v = 3.2. If the linear shape ατ ² is plotted as a function of v, this results in the curve shown in FIG. 3. The dots mark the value ν = 3.2 of a commercially available “real” laser, corresponding approximately to the value of the linear shape parameter αα ² = 0.38. limits of about ² ατ ν → ∞ is ατ ² = 1/12 (or ατ ²

0.083), only a slight improvement over v = 4.5 can be achieved.

Even in the limitation on the Lorentz functions modified as conceivable spectral line shapes, α ² can thus be improved by more than three times compared to the reference laser.

If other spectral linear shapes, in particular parabolic shapes, are allowed, further improvements are even more possible, which will be explained below.

0.26의 결과를 가져오며, ν의 연산적 적합(computational fit)을 통하는 우회는 대략적으로 ατ² = 0.36의 결과를 가져온다(도 3 참조).In order to be accurate in the range of ν = 3.2 to ν = 3.75, there are different indications for ν for different commercially available lasers. The differences can be attributed only to the part of the lasers, but assume that they can be attributed to other parts for measurement and evaluation. It thus remains to assess how large the improvement potential for the individual lasers is. The integrated integration of the measured laser profiles for XLA-360 is ατ ²

The result is 0.26, and the bypass through the computational fit of ν results in approximately α ² = 0.36 (see FIG. 3).

0.083 및 포물선 형상에 대해서 9/125

0.072와 비교되어야 한다.These numbers are the limits 1/12 for the modified Lorenz function.

9/125 for 0.083 and parabolic shapes

It should be compared with 0.072.

To clarify some of the advantages of the present invention, simple examples are shown here with reference to FIG.

0.083)이다.The linear shape I (ω) shown in FIG. 4A is considered to be a flat top (spectral) with a width Δ. It is a case where the then α = Δ ^2/12 is resulting from the equation (1), τ = 1 / Δ resulting from equation (4). The product or linear shape parameter is thus ατ ² = 1/12 (

0.083).

가 방정식 (4)로부터 초래된다. 곱 또는 선 형상 파라미터 ατ²는 따라서 ατ² = 1/(4π)

0.080이다.If (as a function of frequency) having a width σ is assumed Gaussian curve in place with respect to I (ω) (Fig. ^{4b), α = σ 2/} 2 is resulted from the equation (1)

Results from equation (4). The product or linear parameter ατ ² is thus ατ ² = 1 / (4π)

0.080.

The product ατ ² is therefore somewhat smaller for the Gaussian curve than for the flat top. Thus, some shorter coherence lengths and thus less staining can be achieved for constant chromatic aberration imparted by a Gaussian curve. Alternatively, given the same blot, chromatic aberration can be reduced if a Gaussian curve is used instead of a flat top. In other words: If it is important to reduce the influence of temporally varying blobs on image generation as compared to conventional systems and methods, without increasing the effect of chromatic aberration on image generation simultaneously, a laser line with a Gaussian shape may be used for optical lithography. Better fit than a flat top

Conditions under which the product ατ ² according to equations (1) and (4) are intended to be minimized create a mathematically well defined problem. The optimized line shape below was determined by Monte Carlo simulation. The laser line in this optimized variant has the shape of a cut-off parabola (see also FIG. 4C).

0.072에 대응한다. 상이한 곡선 형상들에 대한 곱들(선 형상 파라미터들) ατ²는 따라서For this curved shape, α = Δ2 / 5 and τ = 3 / (5Δ), and the resulting product ατ ² is ατ ² = 9/125 and ατ ²

Corresponds to 0.072. The products (linear shape parameters) ατ ² for different curved shapes are thus

0.083Flat Top: ατ ² = 1/12

0.083

0.080Gaussian curve: ατ ² = 1 / (4π)

0.080

0.072Parabolic Geometry: ατ ² = 9/125

0.072

Parabolic shapes are thus actually better than Gaussian profiles or flat top profiles.

The examples indicate that for the problem described herein, it is important that it occurs in the areas on the side of the intensity profile. For example, if 1% of the total energy in the sides is shifted, this has the effect of being larger digits than if 1% of the total energy in the line core is shifted. Thus, the laser line shape should have a lateral contribution of least likelihood, where the term “side” here represents substantially the transition region between the line core and the line wing. In this respect, the Gaussian curve has a wider side than the parabola-the sides theoretically go infinity in the case of Gaussian curves, but they only have a finite range in the case of parabolic. If, in contrast, the sides are completely cut off as in the case of a flat top, the part of the core is now a side, since everything outside is eventually of the side type. In the case of a flat top, the area | region which has very high intensity | strength thus becomes a side surface. Parabola is therefore a very good compromise on the background of the underlying problem.

Referring to Fig. 5, one possibility to influence the spectral line shape in the case of an excimer laser will be given based on an example. Excimer lasers are currently the main light source used principally for microlithography in the DUV and VUV domains. Excimer lasers vary many different spatial modes and have a low degree of spatial coherence compared to other types of lasers. In addition, a relatively broad spectrum is emitted, which means low temporal coherence. An additional factor is the significantly higher emission power than in the case of normal non-laser sources in the UV region. The inherent bandwidth of an excimer laser can be in the range of hundreds of pm and therefore must be significantly narrowed to yield a narrow bandwidth suitable for microlithography. Therefore, the excimer laser for microlithography is equipped with a so-called bandwidth narrowing module. In the case of the laser radiation source from FIG. 5, the bandwidth narrowing module 510 has the function of forming a backward resonator termination of the laser and reducing the bandwidth of the laser radiation emitted by wavelength-selective reflection. . In the vicinity of the rear coupling-out window of the augmentation or gas discharge chamber 520 is a beam extension 512 comprising four suitably arranged prisms lined up. The expanded laser beam impinges on an echelle grating 530 in a Lettrow configuration, whereby the incident extended laser beam is reflected on itself. This basic configuration is known per se. The spectral line profile of the laser is now substantially determined by the spectral reflectance of the essel grating 530. By blazed ruling of the grating, or in some other way, the height profile of the grating can be defined during the manufacture of such a way to create the required spectral intensity distribution in the emerging laser beam 550. .

In an exemplary embodiment, the height profile of the essel grating 530 is open downwards where the laser radiation 550 emitted by the laser 500 can be substantially parameterized by the technique shown in equation (10). It is designed to have a parabolic spectral line shape.

The required spectral line shape of the emitted laser beam is predetermined during manufacture of the reflective grating 530 for the bandwidth narrowing module. The height profile of the reflective grating that contributes to this linear shape is determined therefrom by back-calculation. The reflective grating is then made by manufacturing methods known per se, such as blazed ruling.

의 배수만큼의 얼룩 감소를 의미한다. 동일한 얼룩 감소는, 이것이 대략 20%만큼의 트랜스미션(transmission)을 감소시킬지라도, 펄스 연장기(pulse stretcher)에 의해 펄스 길이를 배증하는 것에 의해 또한 달성될 수 있다. 대조적으로, 코히어런스 시간을 감소시킬 목적을 위한 대역폭에 있어서의 증가는 오브젝트에 있어서의 더 나은 컬러 교정을 위한 돈이 많이 드는 수단을 필요로 할 것이다. 대조적으로, 레이저의 스펙트럼 시간 형상의 제안된 설정은 상대적으로 부정적인 결과를 갖지 않는 기술적인 수단이다.It has been shown how the lithographic process can be improved by the proper setting of the spectral line shape. A multiple of 4 of the linear shape parameter ατ ^2- given the same chromatic aberration-is a coherence time shorter than multiple 2, and therefore

Means stain reduction by multiples of. The same blob reduction can also be achieved by doubling the pulse length by a pulse stretcher, although this reduces the transmission by approximately 20%. In contrast, an increase in bandwidth for the purpose of reducing coherence time will require costly means for better color correction in the object. In contrast, the proposed setting of the spectral temporal shape of the laser is a technical means with no relatively negative consequences.

Claims (22)

For exposure of a radiation-sensitive substrate arranged in an area of the image surface of the projection objective lens in which a mask of the pattern of at least one image is arranged in the area of the object surface of the projection objective lens. As a projection exposure method,
Generating laser radiation having a spectral intensity distribution I (ω) according to the angular frequency ω, wherein the laser radiation is

Aberration parameter α and

Characterized by a coherence time τ according to;
Introducing the laser radiation into an illumination system to produce illumination radiation directed to the mask; And
Imaging the pattern onto the substrate with the aid of a projection objective,
The spectral intensity distribution is set such that the condition ατ ² ≤ 0.3 is true for the line shape parameter ατ ² . The method according to claim 1,
The spectral intensity distribution is set such that the condition ατ ² ≤ 0.1 is true for the linear parameter ατ ² . The method according to claim 1 or 2,
The spectral intensity distribution I (ω) corresponds to the half value width of the Gaussian curve, and σ, α = σ ^2/2 and

Is true for the Gaussian curve. The method according to claim 1 or 2,
The spectral intensity distribution I (ω) has a parabolic shape. The method according to claim 1 or 2,
The maximum of the spectral intensity distribution lies in an ultraviolet region of a wavelength shorter than 260 nm. A projection exposure apparatus for exposing a radiation-sensitive substrate arranged in an area of an image plane of a projection objective lens in which a mask of a pattern of at least one image is arranged in an area of an object plane of a projection objective lens,
A main laser radiation source for emitting laser radiation;
An illumination system for receiving said laser radiation and for producing illumination radiation directed to said mask;
The projection objective lens for generating an image of the pattern in an area of the image plane of the projection objective lens,
The laser radiation source is designed to produce laser radiation having a spectral intensity distribution I (ω) according to the angular frequency ω, wherein the laser radiation is

Aberration parameters α and

Can be characterized by a coherence time τ;
The spectral intensity distribution is set so that the condition ατ ² ≤ 0.3 is true for the linear parameter ατ ² . The method of claim 6,
The spectral intensity distribution is set such that the condition ατ ² ≤ 0.1 is true for the linear parameter ατ ² . The method according to claim 6 or 7,
The spectral intensity distribution I (ω) corresponds to the half value width of the Gaussian curve, and σ, α = σ ^2/2 and

Is a true true of the Gaussian curve. The method according to claim 6 or 7,
The spectral intensity distribution I (ω) has a parabolic shape. The method according to claim 6 or 7,
The maximum of the spectral intensity distribution lies in a deep ultraviolet region of wavelength shorter than 260 nm. A laser radiation source for generating laser radiation having a spectral intensity distribution I (ω) according to the angular frequency ω for use in the projection exposure apparatus according to claim 6 or 7,
The laser radiation,

Aberration parameters α and

Can be characterized by the coherence time τ,
The spectral intensity distribution is set so that the condition ατ ² ≤ 0.3 is true for the linear parameter ατ ² . The method of claim 11,
The spectral intensity distribution is set so that the condition ατ ² ≤ 0.1 is true for the linear parameter ατ ² . The method of claim 11,
A reflection grating for wavelength-selective reflection of laser radiation of a resonator of the laser radiation source, such that the spectral intensity distribution of the laser radiation is determined by the spectral reflectivity of the reflective grating A bandwidth narrowing module, wherein the height profile of the reflective grating results in the spectral intensity distribution I (ω) with the linear parameter ατ ² , where the condition ατ ² ≦ 0.3 is true. Laser radiation source, defined to be. A bandwidth narrowing module for a laser radiation source according to claim 11,
A reflecting grating for wavelength-selective reflection of laser radiation of the resonator of the laser radiation source such that the spectral intensity distribution of the laser radiation is determined by the spectral reflectance of the reflecting grating, wherein the height profile of the reflecting grating is Characterized in that the spectral intensity distribution I (ω) according to the frequency ω is defined to result in laser radiation,
The laser radiation,

Aberration parameters α and

Can be characterized by the coherence time τ,
The bandwidth narrowing module, wherein the condition ατ ² ≤ 0.3 is true for the linear parameter ατ ² . The method according to claim 14,
Height profile of the reflection gratings, and the spectral intensity distribution I (ω) is designed to correspond to the Gaussian curve of the half value width σ, α = σ ^2/2 and

Is narrow in the case of the Gaussian curve. The method according to claim 14,
The height profile of the reflective grating is designed such that the spectral intensity distribution I (ω) has a parabolic shape. The method according to claim 5,
The maximum of the spectral intensity distribution lies in the ultraviolet region at a wavelength of 193 nm. The method of claim 10,
The maximum of the spectral intensity distribution lies in the far ultraviolet region of a wavelength of 193 nm. The method of claim 11,
The spectral intensity distribution I (ω) corresponds to the half value width of the Gaussian curve, and σ, α = σ ^2/2 and

Is true for the Gaussian curve. The method of claim 11,
Wherein the spectral intensity distribution I (ω) has a parabolic shape. The method of claim 11,
The maximum of said spectral intensity distribution lies in the far ultraviolet region of wavelength shorter than 260 nm. 23. The method of claim 21,
The maximum of said spectral intensity distribution lies in the far ultraviolet region of 193 nm wavelength.

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